In 2002, it was thought that menopausal hormone therapy using estrogen alone increases breast cancer risk, although not as quickly as combined estrogen plus progestin. Current thinking about estrogen alone is that it reduces breast cancer risk. This is just one example of changing concepts about menopausal hormone therapy and breast cancer outlined in an article the Journal of the National Cancer Institute by Rowan T. Chlebowski, MD, PhD, of the Los Angeles Biomedical Research Institute at Harbor, University of California Los Angeles Medical Center in Torrance, and Garnet L. Anderson, PhD, of the Fred Hutchinson Cancer Research Center in Seattle.
“Recent results from large prospective cohort studies and the Women’s Health Initiative randomized placebo-controlled hormone therapy trials have substantially changed concepts regarding how estrogen alone and estrogen plus progestin influence breast cancer,” Drs. Chlebowski and Anderson stated. “In the [Women’s Health Initiative] trials, fewer breast cancers were seen in postmenopausal women with a previous hysterectomy who were receiving estrogen alone. In contrast, estrogen plus progestin statistically significantly increased breast cancer incidence and breast cancer mortality,” they noted.
“Although the absolute risk of death due to breast cancer associated with estrogen plus progestin use is relatively modest, from a public health perspective, a near doubling of breast cancer deaths with estrogen plus progestin represents a considerable concern,” they wrote.
In addition, the risks of developing breast cancer continue to increase the longer the hormones are used. The authors caution that “findings are limited to the duration of intervention and adherence achieved in the trials; cancer effects of longer duration hormone therapy cannot be inferred from these data.” They also noted that “the different effects of estrogen plus progestin vs estrogen alone on breast cancer are not completely understood.” ■
Cheblowski RT, Anderson JL: J Natl Cancer Inst 104:517-527, 2012.